Odorant for gaseous fuels



Patented Jan. 13, 1953 ODOR/ANT FOR GASEOUS FUELS Howard B. Pollock, San Francisco, Calif., assignor, by mesne assignments, to California. Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Application November 6, 1950, Serial No. 194,385

3 Claims.

This invention relates to a new and improved odorant for gaseous fuels.

Many gaseous fuels, for example, natural gas, do not possess any physical characteristic which renders their presence in small amounts readily perceptible to the senses. Pipe lines through which the gas is transported and equipment in which it is used commonly develop leaks which may permit the escape of appreciable volumes of the gas and the formation of explosive mixtures of the escaping gas with air. In order to render such leaks readily detectable and to avoid the explosive and toxic hazards which may result from the escape of the gas, it is the practice to incorporate in the gaseous fuel a highly odorous chemical.

Since the addition of odorants in no way enhances the value of the fuel from a purely utilitarian point of View, the producer or distributor of the gas is forced to engage in purposeful contamination of his product in order to make its presence in very small amounts readily detectable. An ideal odorant would be a material which provided the gaseous fuel with a characteristic and distinctive odor without affecting any other property f the gas. While the development of the odorant art has been directed toward such an ideal material, the odorants heretofore developed fall far short of the mark in several respects.

Odorants are evaluated in terms of a number of properties which give a measure of their approach to the ideal odorant above referred to. These properties include odor, stability, potency, volatility and boiling range, sulfur contribution of a sulfur-containing odorant to the fuel, corrosivity, tendency to form gum, and toxicity. The odorants currently in commercial use are all sulfur compounds. These generally fall into two classes. Various mercaptans and mixtures of mercaptans containing 1 to 5 carbon atoms constitute one class and sulfur compounds separated from sulfuric acid sludges formed during the treatment of various petroleum fractions with sulfuric acid as described in U. S. Patent No. 2,0.64..8.Q5 to Hampton and Ru h ford constitu he other.

- The. Hampton-Rutherford odor-ant is a volatile Oil obtained from sulfuric acid sludges formed during the treatment of sulfur-bearing mineral oils, especially light, distillates from crude oil or light cracked distillates, with sulfuric acid. The sludge is decomposed by pressure hydrolysis to liberate an oil phase and the odorant is obtained by distillation or steam distillation of the oil phase. The distillate fraction which constitutes the odorant boils within the range of F. to 600 F. and has a sulfur content above 2% and usually in the range 6 to 12% by weight. The active odorizing components of this odorant are believed to be principally organic sulfides of the saturated heterocyclic ring type. This odorant has proven highly successful in commercial practice and millions of pounds of it have been sold and incorporated in gaseous hydrocarbon fuels prior to their introduction into transmission and distribution lines. It is markedly superior to the mercaptans in respect to thermal stability and in resistance to oxidation by traces of oxygen which commonly contaminate commercial fuels. This odorant has two disadvantages: (1) The amount required to be added is ordinarily from 2 to 3 gallons per million cubic feet of gas, an amount which requires the user to provide a considerable storage capacity and bulky odorizing equipment, and (2) the advent of high pressure transmission lines introduces a problem of condensation of the heavier components of the odorant.

Persistent attempts have been made to improve the Hampton-Rutherford odorant by isolating an active component or components from it and by separating a lower boiling more volatile fraction which would be less condensable. It has thus far been impossible to concentrate the active components of the odorant and, rather surprisingly, it has been found that when the whole odorant which boils over a range of; 200 to 300 Fahrenheit degrees is separated into three or more distillation cuts of approximately equal boiling range spread, each of the individual cuts is notably less potent in odor than the whole odorant.

It has now been discovered that an odorant very closely approaching the above described ideal odorant in its properties may be prepared by blending together approximately equal parts of the Hampton-Rutherford odorant and tetrahydrothiophene. The resultant new odorant contains as its active components (1) a volatile oil having a total sulfur content above 2 by weight, preferably from 4; to 7% by Weight, and a distillation range between about 100 and 600 F., preferably between 100 and 400 F., produced by decomposing acid sludge formed during treatment of a sulfur-bearing mineral oil with sulfuric acid to liberate an oil and distilling that oil, and (2) tetrahydrothiophene. The weight ratio of the volatile oil to tetrahydrothiophene in the odorant is in the range 0.4-2.4 to 1.0. In an attractive embodiment ofthis odorant a minor amount of a low-boiling mercaptan, i. e., mercaptan containing 2 to 6 carbon atoms, or of a mixture of low-boiling mercaptans equivalent to 0.1 to 1% by weight of the volatile oil component is desirably added to the volatile oil and tetrahydrothiophene.

Commercial tests of the new odorant have demonstrated that it is thoroughly effective when employed in the amount of one pound per million cubic feet of gas. At this concentration the odor intensity is equivalent to that attained with the Hampton-Rutherford odorant using 2 to 3 gallons per million cubic feet and the character of the odor is very similar to that of the Hampton-Rutherford odorant; in its most practical aspect the character of the odor is such that it is described by the layman as gassy.

Numerous room tests were made employing the odorant of this invention. Unfortunately, no measuring stick has been devised which makes it possible to assign purely objective numerical values to odor intensity, character, etc., and the practice followed in testing and screening odorants is to assemble a group of experienced observers, record their independent evaluations of odor strength and character and then evaluate the odorant for strength and character by comparing their independent observations. Odorant concentration and odorized gas concentration are of course quantitatively controlled. On the basis of a series of such tests, it was concluded that the odorant of the present invention had a medium to strong intensity when observed in a test room containing 0.8% by volume of a gas containing 1 pound of the odorant per million cubic feet of gas. It was found by the room tests that if the content of tetrahydrothiophene in the odorant was below about 30% by weight, odor intensity fell off rapidly and, if the odorant contained more than about 70% by weight of tetrahydrothiophene, intensity dropped and the character of the odor was distinctly less gassy.

A sample of odorant was prepared for a field test by mixing equal weights of the Hampton- Rutherford odorant and tetrahydrothiophene. The Hampton-Rutherford odorant employed was a commercial stock meeting the folowing specifications:

70-80% volatile oil from sludge decomposition. '3020% paraflinic hydrocarbons, 150-300 F. boiling range. 0.30.4% C2-C mercaptans.

Gravity. API. ASTMD287 46.0-56.0. Distillation. ASTHD86 50% recovered 257 F. maximum. 70% recovered 292 F. maxlmum. 90% recovered 345 F. maximum. End poin 400 F. maximum.

93% minimum. 4.5% (by wt.) minimum. 6 lbs. maximum.

Sulfur, ASTMD129 Vapor pressure, Reid, ASTM- Trace, maximum. Acid and caustic, SM 100 drothiophene was separated from the spent sodium sulfide solution by steam stripping and phase separation of the distillate.

The tetra- Thermal decomposition temp. F Sulfur contribution gr./1OO CF .14

Viscosity at 77centistokes .82 Distillation range F. start 200 50% 209 70% 27 a 330 End 360 Weight-pounds/gal 7.31

The field test was of 56 days duration. Papico odorizer was located at a main distribution point. The odorant was introduced into the gas at this point. From the main distribution point the gas was conducted through 12 and 8 inch pipe to two communities in which it was distributed to customers. One community was 24 pipe line miles from the main distribution point and the other was 44 pipe line miles from the main distribution point. No drip or knockout pots were contained in the lines. The interior of the pipe was noted to be clean and bright at the time of an inspection several months prior to the field test. During the test the pipe line pressures varied between 200 and 300 p. s. i. g. The gas flow varied between 13 million cubic feet per day and 20 million cubic feet per day during the test and 26,000 customer meters were served in the two communities. During the test the amount of the odorant introduced into the gas was deliberately varied from an initial amount of 1 pound per million cubic feet at the start to 2 pounds per million cubic feet at the end of the test. During the first half of the test the average amount of odorant introduced was 1.33 pounds per million cubic feet and during the last half of the test the amount averaged 1.86 pounds per million cubic feet. During the 56 day test, room tests were periodically conducted at the terminals of the two lines by metering gas into a room until the gas concentration in the room was 1%. Seven experienced observers rated the odorant intensity at medium to strong during these tests. The effectiveness of the odorant was also checked by personnel of the gas company in whose lines the test was made. These people uniformly reported that the odor as determined at their homes was readily detectable and adequate. During the tests leak complaint statistics were kept and compared with statistics for the same season of previous years during which the Hampton-Rutherford odorant was in use. The leak complaint data indicated that the odorant of this invention when employed in amounts from 1 pound to 1.25 pounds per million cubic feet was at least equivalent in effectiveness to the Hampton-Rutherford odorant employed in amounts of 2 gallons per million cubic feet. During the test, no difficulties were encountered which could be attributed to condensation of the odorant in the transmission or distribution lines.

The odorant of this invention has a high degree of thermal stability, a high resistance to oxidation by small amounts of oxygen which commonly contaminate a gaseous fuel, being in these respects markedly superior to the mercaptan type of odorants. No fading of the odor due to decomposition and no corrosion of the lines were noted.

The odorant of the present invention combines a degree of potency at least equal to the best mercaptan odorants on a comparative weight basis with the high stability and desirable "gassy odor of the Hampton-Rutherford odorant. All of the desirable properties of the Hampton-Rutherford odorant are retained and the two undesirable characteristics of the Hampton-Rutherford odorant, i. e., the large volume required to be used and the tendency to condense in high pressure transmission lines are overcome. The amount of the present odorant necessary to adequately odorize a gas is approximately & the weight of the Hampton-Rutherford odorant which is commonly used, and the 50% point of the present odorant is approximately 100 Fahrenheit degrees lower than the 50% point of the Hampton-Rutherford odorant.

I claim:

1. An odorant for gaseous fuels consisting essentially of approximately equal parts by weight of a volatile oil having a total sulfur content above 2% by weight and a distillation range between 100 F. and about 400 F. produced by decomposing acid sludge formed during the treatment of a sulfur-bearing mineral oil with sulfuric acid to separate an oil phase and distilling said oil phase, and tetrahydrothiophene, said odorant being characterized by the capacity to effectively odorize a gaseous fuel when employed at concentrations below 2 pounds per million cubic feet of gas.

2. An odorant for gaseous fuels consisting essentially of about 30% to 70% by weight of a volatile oil having a total sulfur content above 2% by weight and a distillation range between 100 F. and about 600 F. produced by decomposing acid sludge formed during the treatment of a sulfur-bearing mineral oil with sulfuric acid to separate an oil phase and distilling said oil 6 phase, and to 30% by weight of tetrahydrothiophene, said odorant being characterized by the capacity to effectively odorize a gaseous fuel when employed at concentrations below two pounds per million cubic feet of gas.

3. An odorant for gaseous fuels consisting essentially of approximately equal parts by weight of tetrahydrothiophene and of a volatile oil having a total sulfur content above 2% by weight and a distillation range between F. and about 600 F. produced by decomposing acid sludge formed during the treatment of a sulfur-bearing mineral oil with sulfuric acid to separate an oil phase and distilling said oil phase, and containing from 0.1 to 1.0% by weight based on the volatile oil component of a material selected from the group consisting of mercaptans containing 2 to 6 carbon atoms per molecule and mixtures thereof, said odorant being characterized by the capacity to effectively odorize a gaseous fuel when employed at concentrations below two pounds per million cubic feet of gas.

HOWARD B. POLLOCK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,032,431 Odell Mar. 3, 1936 2,064,805 Hampton et al. Dec. 15, 1936 2,094,270 Hampton et a1. Sept. 28, 1937 OTHER REFERENCES Steinkopf, Chemie des Thiophens, page 104, Edwards Lithoprint of 1941 pub. 

1. AN ODORANT FOR GASEOUS FUELS CONSISTING ESSENTIALLY OF APPROXIMATELY EQUAL PARTS BY WEIGHT OF A VOLATILE OIL HAVING A TOTAL SULFUR CONTENT ABOVE 2% BY WEIGHT AND A DISTILLATION RANGE BETWEEN 100* F. AND ABOUT 400* F. PRODUCED BY DECOMPOSING ACID SLUDGE FORMED DURING THE TREATMENT OF A SULFUR-BEARING MINERAL OIL WITH SULFURIC ACID TO SEPARATE AN OIL PHASE AND DISTILLING SAID OIL PHASE, AND TETRAHYDROTHIOPHENE, SAID ODORANT BEING CHARACTERIZED BY THE CAPACITY TO EFFECTIVELY ODORIZE A GASEOUS FUEL WHEN EMPLOYED AT CONCENTRATIONS BELOW 2 POUNDS PER MILLION CUBIC FEET OF GAS. 